Orthopedic drive assemblies are well known in the art. Such drive assemblies may be adapted for various orthopedic procedures such as drilling, screwing, reaming, wire driving, pinning and sawing (both reciprocating and sagittal). Typically a drive assembly is powered by either a rechargeable battery system (e.g. a cordless system) or by a pneumatic system which utilizes compressed fluid to power the device.
The art is replete with cordless rechargeable battery powered drive assemblies for driving orthopedic surgical instruments. Typically, such instruments comprise generally pistol-shaped devices having elongate handle and drive portions. Examples of such drive assemblies comprise: (1) the Orthopower 90 cordless instruments available from Stryker of Kalamazoo, Mich.; (2) the Cordless 200 Reamer, Cordless 800 Wire Driver, Cordless Sagittal Saw or Cordless 450 Orthopedic Drill available from Dyonics of Andover Md., (3) the Maxion.TM. orthopedic drive device, previously sold by the Minnesota Mining and Manufacturing Co. (3M) of St. Paul, Minn.; (4) the Hall Versipower orthopedic instruments available from Hall Surgical of Carpinerina Calif. (associated with Zimmer); and (5) the product known as the 200 Reamer, previously sold by Black & Decker. Cordless battery powered drive assemblies for driving orthopedic surgical instruments are described in U.S. Pat. Nos. 3,734,207; 4,050,528; 4,091,880; 4,441,563; 4,641,076; 4,728,876 and 5,080,983.
Because the batteries in an orthopedic drive device are preferably rechargeable, releasable attachment means are provided in some prior art devices for releasably attaching a battery pack to the rest of the device. Typically, a battery pack is attached to and removed from the handle portion of the device in a direction that is substantially parallel to the axis of elongation of the handle portion. Individual batteries are placed in a housing creating the battery pack which is then attached to the device by being slid in a direction generally parallel to the elongate axis of the handle portion of the device. The battery pack typically includes electrical circuit connection means for connecting the battery pack to electronic circuitry in the device. A device typically secures the battery pack to the rest of the device.
While such releasable attachment means are generally acceptable, they leave room for improvement. One drawback of such a releasable attachment means is that gravity tends to continuously operate on the battery pack to urge it out of the device. Another drawback for some prior devices is that, because of the significant vibration forces encountered during use of the orthopedic drive assembly (particularly during sagittal sawing), the electrical circuit connection means tend to corrode. This type of corrosion is known as fretting corrosion. As used herein, the phrase "fretting corrosion" means surface degradation occurring at the interface of mating electrical contacts which results in the reduction or even loss of electrical continuity.
Fretting corrosion is found in components forming contacts which are allowed to move independently with respect to each other during current flow. This independent movement is believed to cause mechanical abrasion which will wear the surfaces. Gaping between the electrical contacts during electrical flow may result in electrical arcing with attendant generated heat potentially sufficient to melt the surface of the contacts. Pitting, welding and burning may also result. Also, a physical change in the material forming the contacts may occur. Plating for enhanced electrical contact may be lost and carbon deposits may accumulate resulting in reduced electrical continuity.
Because orthopedic drive assemblies are used in surgical procedures which require delicate yet physically demanding tasks, the balance and maneuverability of an orthopedic drive device is also important to surgeons. Hand fatigue is a problem associated with many existing drive assemblies as well as a general difficulty in maneuvering the device during some surgical procedures. Weight distribution and size considerations are believed to contribute to these problems, as the typical cordless rechargeable battery powered drive assembly may be cumbersome to hold and use, particularly during a delicate orthopedic procedure where only the highest quality is tolerated. Size and weight considerations involved in the placement of elements such as the batteries, transmission, electronic control circuitry and motor typically render an existing device difficult to maneuver.
Other prior art drive assemblies are excessively large. Oversized drive assemblies may be difficult to maneuver, particularly during a surgical procedure at a cramped or remote location.